In the recent development of semiconductor technologies, the three-dimensional multilayer technique of stacking elements in the vertical direction to construct three-dimensional structure has attracted attention as a Beyond-Moore technique that is an alternative to More-Moore techniques of increasing integration densities. It is difficult to design a two-dimensional layout of interconnection, which leads to large power consumption. It has been proposed that a three-dimensional interconnection layout in which circuit blocks having various functions are divided into multiple layers, and chips are connected together, can reduce power consumption or increase processing speed. It has also been proposed that the use of wafer level packaging, which is a three-dimensional multilayer technique used in a package, can reduce cost and size.
In particular, electronic apparatuses that employ a camera module, such as a mobile telephone, etc., require a further reduction in size. Such a demand is becoming unsatisfied with a conventional structure in which a solid-state image sensor is provided in a ceramic package and a glass plate is attached to a surface so that the solid-state image sensor is sealed.
Therefore, instead of the conventional package structure in which there is a cavity between the glass and the solid-state image sensor, a structure in which a glass plate is attached directly to microlenses is currently under development. It has been proposed that, in such a cavitviess package structure aimed at reducing profile and size, the microlenses are formed of SiN (silicon nitride), which is an inorganic material that has a high refractive index (highly-refractive), in order to make a difference in refractive index between a resin with which a surface portion of the microlenses that is a cavity is filled and the microlenses (see Patent Literature 1).
When the microlens is formed of SiN, which is transparent and has a high refractive index, SiN has a tendency to cause high membrane stress. Therefore, a problem arises that a defective surface such as a blemish or distortion occurs due to a significant difference in membrane stress between the microlens and the underlying resin. To address this problem, it has been proposed that at least one stress reduction layer is interposed (see Patent Literature 2).